copy from another person called pehjota from channel trisquel;

The comments in that ticket say that OpenWatcom is used because bcc is no longer sufficient for VB's BIOS C code.  VB includes the compiled assembly files generated by OpenWatcom and expects distributions like Debian to use those assembly files (which would allow VB to be built without OpenWatcom). However, those assembly files are not the preferred form for modification, so that trick doesn't mean that VB is free software with only free dependencies. VB still cannot be built from all of its source code with only free tools.

OK:
Open Watcom is not required to build Virtualbox
https://www.virtualbox.org/ticket/12011
Moreover Tuleap do not need Virtualbox to be runned
There is no licensing issue here